It is common, particularly in the small, lightweight, high speed turbomachines which are increasingly being used in a variety of applications, to encounter one or more system resonances in accelerating the rotating components to design speed. If conventional rigid bearing supports are used, the rotating components must be carefully balanced in order for the machinery to pass through the critical speeds with minimum excursion of the rotating members. However, with high operating speeds of many turbomachines, which speeds may be in the range of 36,000 rpm, even relatively small imbalances in rotating components will produce excessive vibration.
Much attention has been devoted to developing so-called "flexible" or "soft" bearing supports, i.e., supports which have a stiffness much less than that of the bearings. Further, since an undamped flexible support system is highly sensitive to external shocks, various damping mechanisms have also been developed.
In order to overcome the disadvantage associated with conventional flexible supports such as rubber O-rings, springs, diaphragms, and the like, and with conventional damping methods such as the use of lubricating oils and elastomers (see, e.g., the U.S. Pat. No. 3,097,167, to Beyerle), hydrostatic bearing systems have been developed. Although this listing is not, nor is it intended to be, exhaustive, such hydrostatic bearings are illustrated in U.S. Pat. Nos. 3,049,383 (Loch); 3,442,560 (de Gast); and 3,499,691 (Baier). These and other conventional hydrostatic bearing systems are characterized by their circular geometries. As a consequence, some means, such as anti-rotation pins, or the like, are required to prevent relative rotation between the bearings and the bearing supports. Moreover, a circular geometry makes it very difficult to vary the dynamic damping characteristic of the hydrostatic supporting film, or to selectively adjust the dynamic stiffness characteristic of portions or particular areas of the supporting film. Conventional hydrostatic bearing systems thus have limited effectiveness in controlling the various rotor unbalance forces generated at different rotor speeds.